Field of the Invention
This invention relates to an improved catalyst for the ammoxidation of propane and isobutane to .alpha.,.beta.-unsaturated mononitriles (acrylonitrile and methacrylonitrile). The preferred application of the invention is in the recycle process in which unreacted propane and isobutane, along with propylene and isobutene produced by the reaction, are recycled back to the reactor for the conversion to acrylonitrile and methacrylonitrile.
Nitriles, such as acrylonitrile and methacrylonitrile, have been industrially produced as important intermediates in the preparation of fibers, synthetic resins, synthetic rubbers and the like. The commercially dominant method for their production requires the ammoxidation of propylene or isobutylene in the presence of ammonia and oxygen at a high temperature in a gas phase in the presence of an ammoxidation catalyst.
However, in view of the price differential between propane and propylene, or the price difference between isobutane and isobutene, recent attention has been drawn to the development of a method and catalyst for the production of acrylonitrile or methacrylonitrile by an ammoxidation reaction wherein the lower alkane such as propane or isobutane is used as a starting material and such lower alkane is catalytically reacted with ammonia and an oxygen-containing gas in the presence of a catalyst.
Earlier attempts to develop an efficient process for the ammoxidation of propane to acrylonitrile produce either insufficient yields or processes that necessitated adding halogen promoters to the feed. The latter procedure would require not only reactors made of special corrosion resistant materials, but also a quantitative recovery of the promoter. This added cost eliminated the advantages of the propane/propylene price differential.
Recent patent publications such as EPO O767164-A1 and patents such as U.S. Pat. Nos. 5,008,427 and 5,231,214 have been directed to ammoxidation catalyst systems which are directed to solving the problems of previous attempts at propane ammoxidation using specific catalyst. In particular, U.S. Pat. No. 5,008,427 and U.S. Ser. No. 09/048,648 both assigned to the assignees of the present invention are specifically directed to a vanadium-antimony promoted catalyst for propane ammoxidation wherein the catalyst is calcined at temperatures of 780.degree. C. or higher. The catalyst in the present invention and the ammoxidation procedure disclosed herein is directed to an improvement in the '427 patent and copending U.S. Ser. No. 09/048,648.